[PATCH v2 15/51] btrfs: comment on direct access bvec table

[Ming Lei <ming.lei@redhat.com>]

Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 fs/btrfs/compression.c |  4 ++++
 fs/btrfs/inode.c       | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 2c0b7b57fcd5..5972f74354ca 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -541,6 +541,10 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 	/* we need the actual starting offset of this extent in the file */
 	read_lock(&em_tree->lock);
+	/*
+	 * It is still safe to retrieve the 1st page of the bio
+	 * in this way after supporting multipage bvec.
+	 */
 	em = lookup_extent_mapping(em_tree,
 				   page_offset(bio->bi_io_vec->bv_page),
 				   PAGE_SIZE);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4ab02b34f029..7e725d84917b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8055,6 +8055,12 @@ static void btrfs_retry_endio_nocsum(struct bio *bio)
 	if (bio->bi_status)
 		goto end;
 
+	/*
+	 * WARNING:
+	 *
+	 * With multipage bvec, the following way of direct access to
+	 * bvec table is only safe if the bio includes single page.
+	 */
 	ASSERT(bio->bi_vcnt == 1);
 	io_tree = &BTRFS_I(inode)->io_tree;
 	failure_tree = &BTRFS_I(inode)->io_failure_tree;
@@ -8146,6 +8152,12 @@ static void btrfs_retry_endio(struct bio *bio)
 
 	uptodate = 1;
 
+	/*
+	 * WARNING:
+	 *
+	 * With multipage bvec, the following way of direct access to
+	 * bvec table is only safe if the bio includes single page.
+	 */
 	ASSERT(bio->bi_vcnt == 1);
 	ASSERT(bio->bi_io_vec->bv_len == btrfs_inode_sectorsize(done->inode));
 
-- 
2.9.4